package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

import org.apache.lucene.util.PriorityQueue;

/**
 * Expert: A hit queue for sorting by hits by terms in more than one field.
 * Uses <code>FieldCache.DEFAULT</code> for maintaining
 * internal term lookup tables.
 * 
 * @lucene.experimental
 * @since 2.9
 * @see Searcher#search(Query,Filter,int,Sort)
 * @see FieldCache
 */
public abstract class FieldValueHitQueue<T extends FieldValueHitQueue.Entry> extends PriorityQueue<T> {

    public static class Entry extends ScoreDoc {
        public int slot;

        public Entry(int slot, int doc, float score) {
            super(doc, score);
            this.slot = slot;
        }

        @Override
        public String toString() {
            return "slot:" + slot + " " + super.toString();
        }
    }

    /**
     * An implementation of {@link FieldValueHitQueue} which is optimized in case
     * there is just one comparator.
     */
    private static final class OneComparatorFieldValueHitQueue<T extends FieldValueHitQueue.Entry> extends FieldValueHitQueue<T> {

        private final FieldComparator comparator;
        private final int oneReverseMul;

        public OneComparatorFieldValueHitQueue(SortField[] fields, int size) throws IOException {
            super(fields);

            SortField field = fields[0];
            comparator = field.getComparator(size, 0);
            oneReverseMul = field.reverse ? -1 : 1;

            comparators[0] = comparator;
            reverseMul[0] = oneReverseMul;

            initialize(size);
        }

        /**
         * Returns whether <code>a</code> is less relevant than <code>b</code>.
         * @param a ScoreDoc
         * @param b ScoreDoc
         * @return <code>true</code> if document <code>a</code> should be sorted after document <code>b</code>.
         */
        @Override
        protected boolean lessThan(final Entry hitA, final Entry hitB) {

            assert hitA != hitB;
            assert hitA.slot != hitB.slot;

            final int c = oneReverseMul * comparator.compare(hitA.slot, hitB.slot);
            if (c != 0) {
                return c > 0;
            }

            // avoid random sort order that could lead to duplicates (bug #31241):
            return hitA.doc > hitB.doc;
        }

    }

    /**
     * An implementation of {@link FieldValueHitQueue} which is optimized in case
     * there is more than one comparator.
     */
    private static final class MultiComparatorsFieldValueHitQueue<T extends FieldValueHitQueue.Entry> extends FieldValueHitQueue<T> {

        public MultiComparatorsFieldValueHitQueue(SortField[] fields, int size) throws IOException {
            super(fields);

            int numComparators = comparators.length;
            for (int i = 0; i < numComparators; ++i) {
                SortField field = fields[i];

                reverseMul[i] = field.reverse ? -1 : 1;
                comparators[i] = field.getComparator(size, i);
            }

            initialize(size);
        }

        @Override
        protected boolean lessThan(final Entry hitA, final Entry hitB) {

            assert hitA != hitB;
            assert hitA.slot != hitB.slot;

            int numComparators = comparators.length;
            for (int i = 0; i < numComparators; ++i) {
                final int c = reverseMul[i] * comparators[i].compare(hitA.slot, hitB.slot);
                if (c != 0) {
                    // Short circuit
                    return c > 0;
                }
            }

            // avoid random sort order that could lead to duplicates (bug #31241):
            return hitA.doc > hitB.doc;
        }

    }

    // prevent instantiation and extension.
    private FieldValueHitQueue(SortField[] fields) {
        // When we get here, fields.length is guaranteed to be > 0, therefore no
        // need to check it again.

        // All these are required by this class's API - need to return arrays.
        // Therefore even in the case of a single comparator, create an array
        // anyway.
        this.fields = fields;
        int numComparators = fields.length;
        comparators = new FieldComparator[numComparators];
        reverseMul = new int[numComparators];
    }

    /**
     * Creates a hit queue sorted by the given list of fields.
     * 
     * <p><b>NOTE</b>: The instances returned by this method
     * pre-allocate a full array of length <code>numHits</code>.
     * 
     * @param fields
     *          SortField array we are sorting by in priority order (highest
     *          priority first); cannot be <code>null</code> or empty
     * @param size
     *          The number of hits to retain. Must be greater than zero.
     * @throws IOException
     */
    public static <T extends FieldValueHitQueue.Entry> FieldValueHitQueue<T> create(SortField[] fields, int size) throws IOException {

        if (fields.length == 0) {
            throw new IllegalArgumentException("Sort must contain at least one field");
        }

        if (fields.length == 1) {
            return new OneComparatorFieldValueHitQueue<T>(fields, size);
        } else {
            return new MultiComparatorsFieldValueHitQueue<T>(fields, size);
        }
    }

    public FieldComparator[] getComparators() {
        return comparators;
    }

    public int[] getReverseMul() {
        return reverseMul;
    }

    /** Stores the sort criteria being used. */
    protected final SortField[] fields;
    protected final FieldComparator[] comparators;
    protected final int[] reverseMul;

    @Override
    protected abstract boolean lessThan(final Entry a, final Entry b);

    /**
     * Given a queue Entry, creates a corresponding FieldDoc
     * that contains the values used to sort the given document.
     * These values are not the raw values out of the index, but the internal
     * representation of them. This is so the given search hit can be collated by
     * a MultiSearcher with other search hits.
     * 
     * @param entry The Entry used to create a FieldDoc
     * @return The newly created FieldDoc
     * @see Searchable#search(Weight,Filter,int,Sort)
     */
    FieldDoc fillFields(final Entry entry) {
        final int n = comparators.length;
        final Object[] fields = new Object[n];
        for (int i = 0; i < n; ++i) {
            fields[i] = comparators[i].value(entry.slot);
        }
        //if (maxscore > 1.0f) doc.score /= maxscore;   // normalize scores
        return new FieldDoc(entry.doc, entry.score, fields);
    }

    /** Returns the SortFields being used by this hit queue. */
    SortField[] getFields() {
        return fields;
    }
}
